Something else to think about...If we are talking about pipe flange bolting, and if not please ignore me...The only 4" ANSI flange that uses 7/8" studs is a 600# class flange. A 4" 600# flange is barely good enough at your stated 1440 psi system (a 4" 600# flange is P/T rated at 1480 PSI up to 100 degrees F and it falls off to 1350 at 200 degrees F). In the range of temps below 100 F, the B7 would be fine (if non-corrosive atmosphere) but seems to me the flanges need another look, not just bolting.
As for bolting, A193 B7 is good to around 900 F, but I would go with B16 from 800 F to 1100 F, if up to 1500 F go with stainless B8C or such.